The present invention relates to electrical contactors and, more particularly, to a method and apparatus for reducing oxide contamination on contactor tips used in no-load power switching applications. There are numerous applications in which electrical contactors are used to isolate an electrical circuit from an electrical power source. In many of these applications, the contactor is operated in what is sometimes referred to as a dry-switching mode, i.e., in a mode in which no current is drawn through the contactors' tips at the time of opening or closing. For example it is common to use a key switch controlled contactor in electrical vehicles to isolate the battery from the electric traction motor and associated control when the key switch is turned to an off position.
While there are advantages to operating a contactor in a dry switching mode, such as, for example, to extend contactor tip life by eliminating arcing, there is also a significant disadvantage. In particular, contactor tips, typically produced from a silver based metal, will form a surface oxide or sulfide which has poor electrical conductivity and acts as an electrical insulator at such tips. In some instances the oxide or sulfide may accumulate sufficiently to block current flow to the electrical system while a lesser accumulation may reduce available power to the system.
One method of avoiding oxide and sulfide build-up is to construct contactors in which the tips exhibit a wiping action during operation, i.e., a moving tip rubs across a surface of a stationary tip to wipe the oxide from the tip. A disadvantage of such contactors is their relatively high cost in comparison to conventional contactors. Accordingly, it is desirable to develop a means for preventing oxide and sulfide build-up on contactor tips which does not require special contactors.